JP2006526878A - Lithium ion battery with improved high-temperature storage characteristics - Google Patents

Abstract

The present invention provides a positive electrode for a battery containing a metal hydroxide having a large specific surface area as a positive electrode additive. The present invention also provides a lithium ion battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode contains a metal hydroxide having a large specific surface area as a positive electrode additive. . In the present invention, by using a metal hydroxide having a large specific surface area as a positive electrode additive, excellent high-temperature storage characteristics can be achieved even with a small amount of metal hydroxide in a lithium ion battery.

Description

  The present invention relates to a positive electrode for a battery including a positive electrode additive that improves high-temperature storage characteristics of the battery, and a lithium ion battery including the same.

  Lithium ion batteries are used in a high operating voltage range (0 to 5V), so when fully exposed to a high temperature (40 ° C) for a long time after a full charge of the lithium ion battery, a high voltage difference between the positive and negative electrodes As a result, self-discharge occurs, and a decomposition reaction occurs due to the reactivity of the positive electrode with respect to the non-aqueous electrolyte, resulting in a decrease in battery capacity and a rapid increase in battery impedance. This is a big problem of the lithium ion battery.

  In order to solve the above problems, a small amount of an additive is used for the negative electrode, the electrolytic solution, or the positive electrode, or the electrode surface reacts with the electrolytic solution by coating an inorganic substance or an organic substance on the powder surface of the positive electrode or the negative electrode. There have been attempts to mitigate. Japanese Patent Application Laid-Open No. 10-255839 describes that an effect of suppressing a decrease in battery capacity after high-temperature storage can be obtained by mixing an alkaline earth metal hydroxide with a positive electrode active material at a predetermined ratio. ing.

However, there is no description about mixing any metal hydroxide other than alkaline earth metal hydroxide into the positive electrode active material in order to improve the high temperature storage characteristics of the battery.
Japanese Patent Laid-Open No. 10-255839

  In addition, although metal hydroxide is an additive that has a good effect on improving the high-temperature storage characteristics of the battery, when it is added in an excessive amount because it is a nonconductor, the battery capacity may be reduced and the high-temperature storage characteristics may be deteriorated. In addition, since the metal hydroxide cannot occlude / release lithium ions, when the amount of the metal hydroxide added to the positive electrode of the battery is increased, the amount of the positive electrode active material that can be contained in the positive electrode of the battery is reduced. This leads to a decrease in battery capacity. Therefore, it is necessary to minimize the amount of metal hydroxide added to the battery positive electrode in order to minimize battery capacity reduction. In this connection, the relationship between the specific surface area of the metal hydroxide added to the positive electrode of the battery and the high temperature storage characteristics of the battery, and the method by which high temperature storage characteristics can be achieved with a small amount of metal hydroxide. Has not yet been disclosed.

  When the present inventors add a metal hydroxide as a positive electrode additive to the positive electrode of the battery, the high temperature storage characteristics of the battery can be improved, and this effect is related to the specific surface area of the metal hydroxide powder. Found that there is. That is, when a metal hydroxide having a large specific surface area is added as a positive electrode additive to the positive electrode of a battery, the high temperature storage characteristics of the battery can be improved even with a relatively small amount of metal hydroxide. It has been found that the reduction in battery capacity due to the addition of oxide can be minimized.

  Accordingly, an object of the present invention is to provide a positive electrode for a battery and a lithium ion battery containing a metal hydroxide having a large specific surface area as a positive electrode additive.

  The present invention provides a positive electrode for a battery containing a metal hydroxide having a large specific surface area as a positive electrode additive.

The present invention also provides a lithium ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a metal hydroxide having a large specific surface area as a positive electrode additive.
Hereinafter, the present invention will be described in more detail.

  As described above, when the metal hydroxide is used as a positive electrode additive, the present inventors can improve the high-temperature storage characteristics of the battery. We found the fact that the larger the surface area, the better. This is considered to prevent the generation of substances such as LiF and HF that increase the resistance of the battery by the surface of the metal hydroxide acting on other constituent substances in the battery such as an electrolyte. It is done. According to this operation principle, the effect of the present invention is proportional to the surface area of the metal hydroxide that is the positive electrode additive. Such an effect is supported by Examples and Comparative Examples described later.

  Therefore, in the present invention, by using a metal hydroxide having a large specific surface area as a positive electrode additive, excellent high-temperature storage characteristics, that is, battery capacity, even when a relatively small amount of metal hydroxide is added. Minimization of reduction and prevention of increase in impedance can be achieved, thereby minimizing the problem of battery capacity reduction due to increased addition of metal hydroxide.

In the present invention, the metal hydroxide is preferably 1 m ² / g or more, more preferably 2.5 m ² / g, and most preferably 7 m ² / g or more. As described above, the metal hydroxide used as the positive electrode additive in the present invention can exhibit an effect that is superior as the specific surface area is increased. On the other hand, the metal hydroxide is preferably as the specific surface area is large. However, the metal hydroxide may be limited by the state of the art in the technical field such as the condition of the battery to be produced and the technique for preparing the metal hydroxide. In the present invention, the specific surface area of the metal hydroxide is preferably 100 m ² / g or less in consideration of the conditions for coating the positive electrode slurry on the electrode current collector when producing the positive electrode.

Examples of the metal hydroxide that can be used in the present invention include Al (OH) ₃ , Mg (OH) ₂ , Ca (OH) ₂ , LiOH, NaOH, and the like. It is preferably included in the following amounts. When the metal hydroxide is added to the battery positive electrode even in a very small amount, the high-temperature storage characteristics of the battery can be improved. There is a problem that the battery capacity decreases due to the increase in resistance due to the conductor properties, and the high-temperature storage characteristics deteriorate. Further, when added to the positive electrode in an amount of 10% by weight or more, the content of the positive electrode active material capable of inserting and extracting lithium ions is relatively reduced, which leads to a reduction in battery capacity. Such a fact is also expressed in the results of Examples described later (Examples 1 to 5 and Comparative Example 1).

  The positive electrode of the present invention is prepared by mixing a positive electrode active material and a positive electrode material including the metal hydroxide having a large specific surface area in a solvent to prepare a positive electrode slurry, and then applying the slurry to a positive electrode current collector. It can be produced by drying.

In the present invention, a lithium-containing transition metal compound can be used as the positive electrode active material. As non-limiting examples, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCoPO ₄ , LiNi _{1 can be used. -X} Co _X M _Y O ₂ (where, M = Al, Ti, Mg , Zr, 0 <X <1,0 <Y <0.2), LiNi X Co Y Mn 1-X-Y O 2 ( Here, 0 <X < 0.5, 0 <Y < 0.5), and LiMxM′yMn _(2-xy) O ₄ (M, M ′ = V, Cr, Fe, Co, Ni, Cu , 0 <X < 1, 0 <Y < 1). These may be used alone or in combination of two or more.

  The present invention also provides a lithium ion battery including the positive electrode of the present invention. The lithium ion battery of the present invention can be produced using materials and methods known in the art except that a metal hydroxide having a large specific surface area is added as a positive electrode additive to the positive electrode. . For example, in the lithium ion battery of the present invention, an electrode body formed by laminating a porous positive separator film between a positive electrode and a negative electrode is accommodated in a battery case by a normal method, and a non-aqueous electrolyte is injected therein. Can be produced.

In the present invention, as the negative electrode, carbon, lithium metal or an alloy capable of inserting and extracting lithium ions can be used, and a metal oxide capable of inserting and extracting lithium ions and having a potential with respect to lithium of less than 2 V is also used. Can do. Examples of the metal oxide having a potential with respect to lithium of less than 2 V include TiO ₂ , SnO ₂ , and Li ₄ Ti ₅ O ₁₂ .

  Non-limiting examples of electrolytes that can be used in the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) or diethyl carbonate (DEC), dimethyl carbonate (DMC). ), Chain carbonates such as ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC).

In order to further improve the high-temperature storage characteristics of the lithium ion battery, the electrolyte contains at least one additive selected from the group consisting of the following general formula 1, general formula 2, general formula 3, and general formula 4. Can be added.

In the general formulas 1, 3, and 4, R ₁ and R ₂ are each independently hydrogen, C ₁ -C ₅ alkenyl group, C ₁ -C ₅ alkyl group, halogen, and C ₁ -C ₅ alkyl. It is selected from the group consisting of a phenyl group and a phenoxy group substituted or unsubstituted by a group or halogen.

In Formula 2, R _is, C 1 -C ₅ alkenyl _group, a C 1 -C ₅ alkyl group.

  Non-limiting examples of compounds representing general formula 1 include VC (vinylene carbonate) and methyl esters.

  Non-limiting examples of compounds representing general formulas 2-4 include propane sultone (PS), propene sultone, dimethyl sulfone, diphenyl sulfone, divinyl sulfone, methanesulfonic acid, and the like.

  In addition to these electrolytes, usual additives known in the art can be added.

  The outer shape of the lithium ion battery of the present invention may be a cylindrical shape, a square shape, a pouch shape, or a coin shape.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these.

Example 1
A coin-type battery was produced by a conventional method. As the positive electrode active material, LiCoO ₂ 94.9% by weight, Al (OH) ₃ 0.1% by weight with an average particle size of 0.8 μm and a specific surface area of about 11 m ² / g, Super-P (conductive agent) 2.5 % By weight and 2.5% by weight of PVDF (polyvinylidene fluoride binder) are added to NMP (n-methyl-pyrrolidone) as a solvent to prepare a positive electrode mixture slurry, which is then coated on an Al current collector. A positive electrode was produced. In addition, a lithium foil is used as the negative electrode, an EC / EMC-based solution of 1M LiPF ₆ is used as the electrolytic solution, and 2% by weight of VC (vinylene carbonate) and 3% by weight of PS (propane sultone) are used as the electrolytic solution. Was added to make a coin-type battery.

Example 2
A coin-type battery was manufactured in the same manner as in Example 1 except that LiCoO ₂ as the positive electrode active material was 94 wt% and Al (OH) ₃ was 1 wt%.

Example 3
A coin-type battery was manufactured in the same manner as in Example 1 except that LiCoO ₂ as a positive electrode active material was changed to 93% by weight and Al (OH) ₃ was changed to 2% by weight.

Example 4
A coin-type battery was manufactured in the same manner as in Example 1 except that LiCoO ₂ as a positive electrode active material was changed to 90% by weight and Al (OH) ₃ was changed to 5% by weight.

Example 5
A coin-type battery was manufactured in the same manner as in Example 1 except that LiCoO ₂ as a positive electrode active material was 85% by weight and Al (OH) ₃ was 10% by weight.

Example 6
A coin-type battery was fabricated in the same manner as in Example 2 except that Al (OH) ₃ having an average particle size of 1.2 μm and a specific surface area of about 7 m ² / g was used.

Example 7
A coin-type battery was fabricated in the same manner as in Example 3 except that Al (OH) ₃ having an average particle size of 1.2 μm and a specific surface area of about 7 m ² / g was used.

Example 8
A coin-type battery was fabricated in the same manner as in Example 2 except that Al (OH) ₃ having an average particle size of 8 μm and a specific surface area of about 2.5 m ² / g was used.

Example 9
A coin-type battery was manufactured in the same manner as in Example 3 except that Al (OH) ₃ having an average particle size of 8 μm and a specific surface area of about 2.5 m ² / g was used.

Example 10
As shown in FIG. 2, after winding the positive electrode, the porous separator film, and the negative electrode into a roll, a battery housed in a rectangular can as shown in FIG. 3 was used. The details are as follows. As the positive electrode active material, LiCoO ₂ 92.5 wt%, Al (OH) ₃ 2.5 wt% with an average particle size of 8 μm and specific surface area of about 2.5 m ² / g, Super-P (conductive agent) 2.5 wt% % And PVDF (binder) 2.5 wt% were added to NMP (N-methyl-2-pyrrolidone) as a solvent to prepare a positive electrode mixture slurry, which was then coated on an Al current collector. Was made. As the negative electrode active material, artificial graphite is used, and 95.3% by weight of artificial graphite, 0.7% by weight of Super-P (conductive agent), and 4% by weight of PVDF (binder) are added to NMP as a solvent. After preparing a negative electrode mixture slurry, this was coated on a Cu current collector to produce a negative electrode. As the electrolytic solution, an EC / EMC-based solution of 1M LiPF ₆ was used, and 2% by weight of VC (vinylene carbonate) and 3% by weight of PS (propane sultone) were added to the electrolytic solution.

Example 11
Instead an average particle size of using Al _{(OH) 3} the specific surface area at 0.8μm is about ^11m 2 / g, specific surface area average particle size 1.0μm is about _{^{12m 2 / g Mg (OH)}} 2 A coin-type battery was manufactured in the same manner as in Example 2 except that was used.

Example 12
A coin-type battery was fabricated in the same manner as in Example 11 except that Mg (OH) ₂ having an average particle size of 1.5 μm and a specific surface area of about 6 m ² / g was used.

Example 13
A coin-type battery was fabricated in the same manner as in Example 11 except that Mg (OH) ₂ having an average particle size of 9 μm and a specific surface area of about 1.5 m ² / g was used.

Comparative Example 1
A coin-type battery was manufactured in the same manner as in Example 1 except that LiCoO ₂ as a positive electrode active material was 95% by weight and Al (OH) ₃ was not added.

Comparative Example 2
A coin-type battery was manufactured in the same manner as in Example 10 except that LiCoO ₂ as a positive electrode active material was 95% by weight and Al (OH) ₃ was not added.

(High temperature storage experiment)
The batteries produced in Examples 1 to 9 and Comparative Example 1 were charged to 4.2V with a charging current of 1C, and discharged at 1C up to 3V to confirm the initial discharge capacity (A). Was charged again to 4.2 V in the same manner as described above, and then stored at 80 ° C. for 12 hours. After storage, 1C was discharged and the remaining capacity (B) was measured. After the measurement of the remaining capacity, charge / discharge was repeated three times, and then the recovery capacity (C) was confirmed. The initial capacity (A) is compared with the remaining capacity (B) and the recovery capacity (C) in%, and the remaining capacity ratio (= B / A) and the recovery capacity ratio (= C / A), respectively. These are shown in Table 1 and Table 2.

As can be seen from Table 1, when Al (OH) ₃ is contained (Examples 2, 3, 6, 7, 8, and 9), when Al (OH) ₃ is not contained (Comparison) Compared to Example 1), the overall remaining and recovery capacity rates were improved. In addition, when Al (OH) ₃ was added by 1% by weight (Examples 2, 6 and 8), when Al (OH) ₃ was added by 2% by weight (Examples 3, 7 and 9), The recovery capacity rate was much higher.

When compared with the same addition amount (Examples 2, 6 and 8, and Examples 3, 7 and 9), the more specific surface area Al (OH) ₃ is used, the more the remaining capacity and the recovery capacity. It showed a far greater effect. This indicates that the action of Al (OH) _{3 is} an action on the powder surface. Actually, in the case of Example 8 using Al (OH) ₃ having the smallest specific surface area, the residual and recovery capacity ratios show a large difference compared to the case of Comparative Example 1 in which Al (OH) ₃ is not used. It can be seen from the fact that it is not.

As in the case of using Mg (OH) ₂ instead of Al (OH) ₃ as a positive electrode additive (Examples 11 to 13), it is superior to Comparative Example 1 in which no positive electrode additive is added. Showed the effect. In addition, among the examples using Mg (OH) ₂ , the effect of using a material having a large specific surface area was superior.

Therefore, in order to obtain the maximum effect in terms of high-temperature storage characteristics while minimizing battery capacity reduction by adding a metal hydroxide without lithium charge / discharge capability, use powder with a large specific surface area. It is understood that is preferable.

Table 2 shows a comparison result of the residual capacity ratio and the recovery capacity ratio depending on the addition amount of Al (OH) ₃ having a specific surface area of about 11 m ² / g. As shown in Table 2, when 0.1% by weight of Al (OH) ₃ was added to the positive electrode of the battery (Example 1), when Al (OH) ₃ was not added (Comparative Example 1). In the case of adding 5% by weight of Al (OH) ₃ (Example 4), the result is also improved as compared with Comparative Example 1, but 10% by weight of Al (OH) _3. (Example 5) showed a reduced effect as compared with Comparative Example 1. Therefore, in the present invention, the amount of Al (OH) ₃ added as the positive electrode additive is preferably in the range of 0.1 wt% or more and less than 10 wt%.

  In order to evaluate the high-temperature storage characteristics of the batteries produced in Example 10 and Comparative Example 2, a high-temperature storage experiment similar to the above was performed using a square battery. The battery was charged up to 4.2V with a charging current of 1C, and discharged at 1C up to 3V to confirm the initial discharge capacity (A). The cell was again charged to 4.2 V in the same manner as described above, and then the AC impedance was measured (AC impedance before high-temperature storage). AC impedance is a measure that can measure battery performance. The measured value of AC impedance before high temperature storage was almost similar in Example 10 and Comparative Example 2, and was about 60 mohm.

Next, after the battery was stored at 80 ° C. for 10 days, the AC impedance was measured, 1 C was discharged, and the remaining capacity (B) was measured. After the measurement of the remaining capacity, charge / discharge was repeated three times, and then the recovery capacity (C) was confirmed. The residual capacity ratio (= B / A) and the recovery capacity ratio (= C / A) are calculated by measuring the% of the initial capacity (A) and the remaining capacity (B) and the recovery capacity (C). This is shown in Table 3. Moreover, the AC impedance after high temperature storage was compared.

As can be seen from Table 3, when Al (OH) ₃ is contained in the positive electrode (Example 10), an increase in AC impedance after high-temperature storage can be suppressed, and the residual and recovery capacities are also Al (OH) _3. Compared to the case of Comparative Example 2 in which no is used.

  In the present invention, by adding a metal hydroxide having a large specific surface area as a positive electrode additive to the positive electrode of the battery, it is possible to improve the high-temperature storage characteristics of the battery using a small amount of metal hydroxide compared to the prior art. As a result, a decrease in battery capacity due to an increase in the amount of metal hydroxide added can be minimized.

It is sectional drawing of a common coin type battery. FIG. 10 is a schematic diagram showing a storage electrode roll of Example 10. 10 is a schematic diagram showing a rectangular battery can used in Example 10. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode side case 2 Positive electrode collector 3 Negative electrode side case 4 Negative electrode collector 5 Positive electrode 6 Negative electrode 7 Separator film 8 Electrolyte 9 Gasket 1 Positive electrode 2 Separator film 3 Negative electrode 4 Separator film

Claims (7)

A positive electrode for a battery, comprising a metal hydroxide having a specific surface area of 1 m ² / g or more as a positive electrode additive. 2. The positive electrode for a battery according to claim 1, wherein the metal hydroxide has a specific surface area of 2.5 m ² / g or more.   2. The positive electrode for a battery according to claim 1, wherein the metal hydroxide is contained in the positive electrode for a battery in an amount of more than 0% by weight and less than 10% by weight. 2. The battery according to claim 1, wherein the metal hydroxide is at least one selected from the group consisting of Al (OH) ₃ , Mg (OH) ₂ , Ca (OH) ₂ , LiOH, and NaOH. Positive electrode. In a lithium ion battery including a positive electrode, a negative electrode and a non-aqueous electrolyte,
5. The lithium ion battery, wherein the positive electrode is a battery positive electrode according to any one of items 1 to 4. 6. The lithium ion battery according to item 5, wherein the electrolytic solution contains at least one additive selected from the group consisting of compounds represented by the following general formulas 1 to 4.

(In the general formulas 1, 3, and 4, R ₁ and R ₂ are independently of each other hydrogen, C ₁ -C ₅ alkenyl group, C ₁ -C ₅ alkyl group, halogen, and C ₁ -C _5. or substituted alkyl group or halogen, or is selected from the group consisting of phenyl and phenoxy groups being unsubstituted, in the general formula 2, R is, C ₁ -C ₅ alkenyl group or C ₁ -C ₅ alkyl, Group.)   In item 6, the compound of the general formula 1 is selected from the group consisting of VC (vinylene carbonate) and methyl ester, and the compounds of the general formulas 2 to 4 are propane sultone (PS), propene sultone, dimethyl sulfone, A lithium ion battery selected from the group consisting of diphenylsulfone, divinylsulfone, and methanesulfonic acid.

Images